This invention relates to tires and, more particularly, to pneumatic tires provided with novel and highly-effective beads and bead rings.
A pneumatic tire for automotive vehicles generally comprises a crown that comes into contact with the ground and, on either side of the crown, a sidewall the inner edge of which, intended to be supported by the rim of a wheel, is formed by the bead. The bead has among its components at least one bead ring. The latter fulfills various functions. It serves in particular as anchorage for the ply or plies forming the carcass of the tire and withstands the forces exerted on it by the carcass under the effect of the inflation pressure and the deformations resulting from the travel of the tire. The bead ring also serves to ensure the transmission of longitudinal forces and, in the case of tubeless tires, to ensure a seal between the tire and the wheel rim.
Essentially two types of bead rings are used in the manufacture of pneumatic tires: cabled rings and package rings.
The customary cabled rings have a substantially circular cross section. They are produced by means of a continuous wire of circular section or a continuous strand formed of wires of circular section. The wire or the strand is wound helically around a core until the desired cross section is reached. This type of ring is known for its flexibility and its resistance to tearing, by virtue of its cabled structure itself.
Package rings can be made from a continuous wire of circular section, the wire being wound on a suitable support so as to form several superimposed layers of adjoining parallel turns. Alternatively, a package ring can be formed from a ply of adjoining, parallel continuous wires which is wound in such a manner as to constitute several superimposed layers.
The cross section of the package rings may be any desired. In general, this section is adapted as nearly as possible to the architecture and shape of the beads in which the rings are to be arranged.
Despite their simple and economic manufacture, package rings have two defects. The first appears as soon as the tire is introduced into the mold in order to be molded and vulcanized, namely the wires move with respect to each other in the cross section of the bead ring. The result is differences in tension which give rise to the second defect, namely the relatively low resistance to rupture as compared with the cross section of material used.
The instability of shape in cross section of package rings has not been improved by surrounding them at regular intervals with collars which clamp them. This measure does not prevent disorder of the wires between two consecutive collars.
It has also been attempted to replace the layers of wire by a strip of the same cross section, as described in French Pat. No. 1,281,439. With this latter means one can obtain rings of square, rectangular or possibly parallelogram section only. However, these sections also poorly withstand the stresses due to the molding of the bead. The strips slide on each other, since it is difficult to obtain a strip that is perfectly plane on its two major faces at a cost permitting the inclusion thereof in articles in mass production, such as tires. Moreover, it is difficult to obtain from a strip a bead ring having its radially inner wall conical; that is, inclined to the common axis of the tire and ring, as is at times necessary in the case of tubeless tires with bead seats which are themselves conical.